Radio receiving system



Patented Dee. 19, 1939 UNiTED STATES RADIO RECEIVING SYSTEM Gustave L.Grundmann, Westmont, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application August 21, 1937, Serial No. 160,200

7 Claims.

My invention relates to television receivers or the like wherein it isdesired to amplify signals in a plurality of frequency bands.Specifically I have applied my invention to a combination televisionreceiver and broadcast receiver in which the sound signals accompanyingthe picture are in a high frequency band such as a 9.75 megacycle bandand in which the sound signals from broadcast transmitters are in acomparatively low frequency band such as a 460 kilocycle band.

It has previously been the practice in designing combination receiversof the above-mentioned type to employ two separate intermediatefrequency amplifiers for thetelevision sound signals and the broadcastsound signals. These two amplifiers had a common audio amplifier towhich they could be connected selectively by means of suitable switches.For various reasons the feature of switching the two I. F. amplifiers tothe audio amplifier was undesirable. Furthermore, a large number ofamplifier tubes was required for the two separate I. F. ampliers.

It is accordingly an object of my invention to provide an improvedcombination receiver of the above-mentioned type which does not requirethat the audio amplifier be switched to the desired amplifier channel.

It is a furtherobject of my invention to pro- 30'5 vide a simplifiedcombination receiver of the above-mentioned type.

It is a still further object of my invention to provide an improvedamplifier in which one amplifier tube selectively amplies signalsin aplu- 35v rality of frequency bands.

, It is a still further object of my invention to provide an improvedcoupling network for connecting amplifier tubes in cascade relation.

In a preferred embodiment of my invention as 40, applied to a combinedtelevision and broadcast receiver, I supply the television sound signalsand the broadcast sound signals to a common I. F.

amplifier comprising amplifier tubes which are connected in cascade,each tube being coupled 45 to the succeeding tube through two I. F.transformers, one transformer being designed to pass the high frequencytelevision sound signalsI and having the primary and secondary coupledthrough a common coupling coil and the other 50 transformer beingdesigned to pass the comparatively low frequency broadcast soundsignals.

The receiver is provided with switching means whereby either televisionsound signals or broadcast sound signals are supplied to the com- 55.mon I. F. amplifier as desired. The two I. li`

(Cl. Z50-20) transformers in each amplifier stage are so coupled anddesigned that each one is effectively out of the circuit for signals ofthe frequency that the other transformer is designed to pass.

The invention will be better understood from 5 the following descriptiontaken in connection with the accompanying drawings in which Figure l isa circuit diagram of a combined television receiver and broadcastreceiver embodying my invention.

Figures2 and 3 are circuit diagrams which are referred to in explainingthe operation of thereceiver shown in Figure l,

Figure 4 isa circuit diagram of another embodiment of my invention, andv1 Figures 5 and 6 are circuit diagrams which are referred to inexplaining the operationof the circuit shown in Figure 4.

Referring to Fig. l, the combined receiver includes two superheterodynereceiver sections vl and 2, receiver section l being designed forreceiving picture ,signals and the accompanying sound signals on veryhigh frequency carrier waves (40 to 80 megacycles, for example), andreceiver section f2 being designed for receiving 25 sound signals in theordinary broadcast band (550 to 1500 k. c., vfor example).

Receiver section l includes a first detector 3,

a tunable oscillator 4, and a picture amplifier 6 through which picturesignals are supplied to a cathode ray tube l. The usual deflectingcircuits are not illustrated as they form no part of the presentinvention.

l The television sound signals are supplied to an amplifier 8 havingvits output circuit con- 35 nected to an I. F. amplifier which is toamplify both television and broadcast sound signals as will be explainedhereinafter.

The receiver section i may me similar to the corresponding` section ofthe receiver described "40 in Carlson Patent 1,975,056.

The broadcast receiver section 2 includes a radio frequency amplifier 9,a tunable oscillator ll and a first detector l2. The I. F. broadcastsound signals are supplied from the output circuit of detector l2 toYthe first I. F. amplifier tube I3 through a coupling circuit llldesigned in accordance with my invention. .The other I. F. amplifierstages indicated at i6 which supply the I. F. signal to the seconddetector l1 are 50 the same as the preceding stage l3-|4.

The output circuit of the second detector I l is connected to an audioamplifier I8 which supplies either television sound signals or broadcastsound signals to a loudspeaker i9, `depending i515y upon whether soundsignals are supplied from the receiver I or from the receiver 2.

Referring now to the design of the I. F. amplifier I3-Ill, the highfrequency tuned transformer or band pass filter includes a primary coil2I, a secondary coil 22 and a coupling coil 23. The coils 2| and 22 areshunted by tuning condensers 24 and 23, respectively, the exact tuningof the primary and secondary circuits being done by means of movablemagnetic cores in the coilsI 2l and 22. This high frequency transformeris of the type described and claimed in application Serial No. 129,804,filed March 9, 1937, as a joint invention of I-I. C. Allen and G. L.Grundmann, and assigned to the Radio Corporation of America.

For reasons which will appear later, two condensers 2'! and 28 ofcomparatively large capacity are connected in series between coils 2|and 22 and the coupling coil 23 is connected between the junction pointof the two condensers and ground. The condensers 2l and 23 have suchlarge capacity that at the high frequency sound band their effect in thecircuit is negligible.

It will be'seen that the output capacity of detector I2 indicated at 29is across both the primary coil 2I and the coupling coil 23. Likewisethe input capacity of ampliler tube I3 indicated at 3l is across boththe secondary coil 22 and the coupling coil 23. Thus the capacities 23and 3| form part of the tuning capacity of the primary circuit and thesecondary circuit, respectively. Since the inductance of the couplingcoil 23 is small compared with the inductance of primary coil 2I andsecondary coil 22, the fact that condensers 24 and 2G are not across allthe inductance in the primary and secondary circuits, respectively, isnot of importance. As to the relative values of coils 2 I, 22 and 23,coils 2I and 22 may have approximately 25 turns each and coil 23 mayhave 5 turns. It may be noted that in some receiver designs thecondensers 24 and 26 may be omitted and the coils 2| and 22 tunedentirely by the tube capacities 28 and 3 I.

Referring now to the low frequency tuned transformer or band passfilter, it includes a primary coil 32 and a secondary coil 33 which arespaced apart the correct amount to give the desired inductive couplingindicated by the letter M. Plate voltage is supplied to the detector I2through a filter resistor 34, the primary coil 32, a conductor 36 andthe primary coil 2I. A filter condenser 31 is connected between the highpotential end of lter resistor 34V and ground.

The high potential end of secondary coil 33 is connected to the controlgrid 38 of amplifier tube I3 through a conductor 38 and through thesecondary coil 22. The other end of coil 33 is connected to the cathodeil of amplier tube I3 through a suitable biasing source (not shown). Afilter condenser 42 is connected between the low potential end of coil33 and ground.

The primary coil 32 and the secondary coil 33 are effectively shunted bycondensers 21 and 28, respectively, at frequencies in the low frequencyband whereby the primary and secondary circuits are tuned to provide thedesired band pass characteristic. This results from the fact that thecoupling coil 23 presents substantially no impedance to signals in thelow frequency band. Also the lter condensers 3l and 42 are of suchcapacity as to present a low impedance to these signals.

The operation of the coupling circuit I4 will be more clearly understoodby referring to Figs.

2 and 3. In these figures parts corresponding to like parts in Fig. 1are indicated by the same reference numerals.

Referring first to Fig. 2, there is shown the portion of circuit I2which is effective as a band pass filter for signals in the highfrequency band. The coils 32 and 33 of the low frequency transformerpresentl such high impedances to signals in the high frequency band thatthey are effectively out of the high frequency band circuit. Also,condensers 2'I and 28 are effectively out of the high frequency circuitbecause of their low impedance. Therefore, at the high frequency band,the primary circuit comprises coils 2l and 22 tuned by capacities 24 and29 while the secondary circuit comprises coils 22 and 23 tuned bycapacities 26 and 3l. The coupling between the primary and secondarycircuits is provided by the coil 23 which is common to the two circuits.

Referring next to Fig. 3, the effective circuit for signals in the lowfrequency band is as indicated because the coils 2l, 22 and 23 presentsubstantially no impedance to these lower frequencies. It will be seenthat tuning condenser 2l is connected across coil 32 through filtercondenser 3'I and that tuning condenser 28 is connected across coil 33through filter condenser 42. The tube capacities 29 and 3I are inparallel with tuning condensers 2l and 28, respectively.

From the foregoing description it will be apparent that the couplingnetwork I4 functions as a band pass filter for either the high frequencysound band or for the low frequency sound band.

If a picture and the accompanying sound are to be received, the voltagesupply is switched oif the broadcast receiver section 2 by means of anori-off switch I0 thus taking voltage off the screen grid of detector I2whereby it cannot pass signals. Television sound signals are suppliedthrough amplifier 8 and a conductor 43 to the input end of couplingnetwork I4. They then pass through the portion of the circuit shown inFig. 2 to the tube I3, and then through similar I F. stages to thesecond detector I1.

It will be noted that plate voltage is supplied to tube 8 through thesame circuit supplying it to detector I2. Since the output capacity oftube 8, indicated at 42, is in parallel with the tube capacity 2!! it,of course, functions as part of the tuning capacity in the primarycircuit of the high frequency band pass portion of the coupling network.

If the broadcast sound is to be received, the voltage supply is takenoff receiver I whereby there is no voltage on the screen grid of tube 8and no signals are passed by it. The broadcast sound signals appearingin the output circuit of detector I2 pass through the portion of thecoupling network shown in Fig. 3 and through simi lar network portionsto the second detector I1.

It will be evident that my invention permits a saving in the number ofamplifier tubes and that it eliminates the switching of the audioamplifier that would be necessary if two distinct sound I.F. amplifierswere employed.

In Fig. 1 the capacities of condensers 24, 26, 2'! and 28 have beenindicated in micro-microfarads by way of example. 'I'hese values are fora receiver in which the mean frequency of the high frequency pass bandis 9.75 megacycles and in which the mean frequency of the low frequencypass band is 460 kilocycles.

In Fig. 4 there is shown an embodiment of my invention in which the I.F. amplifier feeds into a second detector of the diode type. If thesecond detector is a triode or vthe'like, the circuitjust preceding itmay be the same as the coupling network I4'shown in Fig. 1. However, ifadiode y. detector is'employed certain changes `are de- 5 sirable.

In Fig. 4 parts corresponding to those in Fig. 1 are indicated by thesame reference numerals. In'this figure I have shown a coupling networkM between the final I. Fampliiier tube 46 and the second detector 41 ofthediode type. The output and vinput capacities for tubes 46 and 41 areindicated at 48 and 49, respectively.

' AThe diode detector 41 requires the usual re- I sistor 5| and shunting'condenser 52 connected between the diode cathode and the low potentialend of the secondary coil 33. The audio signal is vtaken from, theresistor 5I asindicated.

It will be seen that if a single coupling coil 1 23 were employed as inFig. 1, the condenser 52 and the condenser 28 wouldl be connected inseries across the secondary 33. This would not be satisfactory becausecondenser 52 cannot be given a capacity large enough to make its imipedance negligible at the low intermediate frequency. In order to avoidthis difficulty I employ coupling coils 53 and 54 in place of the singlecoupling coil 23 shown in Fig. 1.

Each of the coils 53 and 54 has twice the in- `ductance of coil 23.`Since they are effectively in lparallel for signals in the highfrequency band, as will be shown in the following paragraphs, theircombined inductance and coupling action is the same as that of thesingle coil 23. h An additional condenser 56 is connected be-` tweentuning condensers 21 and 28. Coupling coil 53 is connected betweenground and the junction point of condensers 21 `and 56 while couplingcoil 54 is connected between the low potential end of secondary 33 andthe junction point of condensers 28 and 56 through a conductor 55.

Since condenser4 52 has negligible impedance kto signals iny the highfrequency band, the low potential end of secondary 33 is at ground forthese signals. Condenser 56 also has negligible 'vimpedancefor thesesignals. Therefore, coupling coils 53 and 54y are in parallel at thehigh frequencies. i

effective circuit for the high frequency band is shown. Obviously, thiscircuit functions the ?'3 same as the circuit shown in Fig. 2.

In Fig. 6, there is shown the circuit which is effectivev at the lowfrequency band. The tuning condenser?! is connected across coil 32 thesame as shown in Fig. 3. The tuning condenser 56? 28 is connected acrossthe coil 33 through the `conductor 55, the coil 54, like the'coil 53,`being effectively out of the circuit at the lower frequency. 5

It will be noted that in the low frequency band 601i' the condenser 56isin parallel with the by-pass condenser 52 of the. diode circuit.

From the foregoingfdescription it will be lapparent that the secondembodiment of my in- Vention functions in the same way as the firstdescribed embodiment. A receiver having a second detector of the diodetype will ordinarily employ a coupling network such as rthe network I4in Fig. 1 for the I. F. stages up to the last I. F. stage, only thefinal I. F. coupling network being of the type vshown in Fig. 4. y

In Fig. 4 the capacities of condensers 24, 26, 27, 28, 56, and 52 areindicated in micro-microfarads, by way of example, for a networkdesigned to pass the 9.75 megacycle and 460 kilocycle bands.

This is illustrated in Fig. 5 where the f It will be apparent that Ihave provided a combined television and broadcast receiver of simplieddesign.y Also, it will be seen that I have provided a coupling networkcomprising I.' F. transformers for passing different frequency 5 bands,the high frequency transformer` being of a preferred design whichincludes a coupling coil common to the primary and secondary circuitsand the low frequency transformer being of the y inductively coupledtype. 10

I claim as my invention: I

1. An amplifier for passing signals in a comparatively high frequencyband and for passing signals in a comparatively low frequency band, saidamplifier comprising a plurality of amplifier 15' tubes connected incascade through coupling networks,each tube having a plate circuit and agrid circuit, each of said networks including a band pass filter forpassing only the signals in said high frequency band and a band passfilter for passing only the signals in said low frequency band, saidband pass lters being of thevtuned transformer type each having a tunedprimary and a tuned secondary, the primaries being connected in serieswith the plate circuit rof one amplifier tube and the secondaries beingconnected in series with the grid circuit of the succeeding amplifiertube.

2.4An amplifier for passing signals in a high ,i frequency band and forpassing signals in a low frequency band, said amplifier comprising anelectric discharge tube having a plate circuit and an electric dischargetube having an input circuit, Va. network for coupling said tubes, saidnetwork comprising a primary coil of compara- 35' tively high inductanceand a primary coil of comparatively low inductance connected in seriesywith` each other and in series .with said plate circuit, a secondarycoil of comparatively high inductance and a secondary coil ofcomparatively 4,0;Y low inductance connected in series with each otherand in series with said input circuit, said high inductance primary andvsaid high inductance secondary being inductively coupled, two tuningcondensers connected in series and con- 4g;L nected between the junctionpoint of said primaries and the junction point of said secondaries,

a comparatively low inductance coupling coil connected between groundand the junction point of said tuning condensers for coupling said low50i inductance primaryy and said low inductance secondary, said tuningcondensers being of sufficient capacity toltune the high inductanceprimary and the high inductance secondary to pass signals in said low`frequency band, said low in- 515i ductance primary and said lowinductance secondary each being tuned by capacity to pass` signals insaid high frequency band, said two frequency bands differing so widelyinv frequency that said low inductance coilsy present substantially noimpedance to signals in the low frequency band and that said tuningcondensers present substantially no impedance to signals in the highfrequency band.

3. In a combined television and broadcast reg5 ceiver, means forconverting the sound signals accompanying picture signals intointermediate frequency signals having a comparatively high frequency,means for converting the sound signals in the broadcast band intointermediate 70 frequency signals having a comparatively low frequency,an intermediate frequency amplifier comprising a plurality of amplifiertubes connected in cascade, a second detector, means for supplying bothbands of intermediate frequency signals to said second detector throughsaid intermediate frequency amplifier, and an audio amplifier connectedto said second detector, the tubes in said intermediate frequencyamplifier being connected through networks each of which includes a bandpass circuit for the high frequency band and a band pass circuit for thelow frequency band, said band pass circuits being so designed that thecharacteristics of one are substantially independent of thecharacteristics of the other.

4. A coupling circuit for coupling two electric discharge tubes incascade, each of said tubes having an input circuit and an outputcircuit said coupling circuit comprising a primary coil connected to theoutput circuit of one of said tubes to form a primary circuit and asecondary coil connected to the input circuit of another of said tubesto form a secondary circuit, said coils being coupled by means of aninductance coil common to the primary and secondary circuits, saidprimary and secondary coils each having a capacity thereacross to tunethem to pass a band of frequencies at a comparatively high frequency, atransformer having primary and secondary coils which are highlyinductive as compared with said first mentioned primary and secondarycoils and said coupling coil, said primary coils being connected inseries in said output circuit and said secondary coils being connectedin series in said input circuit, a tuning condenser connected betweensaid first primary coil and said coupling coil for tuning said secondprimary coil, and a tuning condenser connected lbetween said firstsecondary coil and said coupling coil for tuning said second secondarycoil, said tuning condensers having such capacity that said transformeris tuned to pass a band of frequencies at a comparatively low frequency.

5. A circuit for coupling two electric discharge tubes, said circuitcomprising a primary circuit Awhich includes a primary coil and acoupling Vcoil in series and means for tuning said primary circuit, asecondary circuit including a secondary coil and said coupling coil inseries and means for tuning said secondary circuit, said primary andsecondary circuits being so tuned and coupled as to pass a band offrequencies having a comparatively high frequency, a tuning condense!connected between said primary coil and said coupling coil, a secondtuning condenser connected between said secondary coil and said couplingcoil, a highly inductive primary coil connected to the junction point ofsaid first primary coil and said first tuning condenser and in serieswith said first primary coil, and a highly inductive secondary coilconnected to the junction point of said first secondary coil and saidsecond tuning condenser and in series with said first secondary coil,said highly inductive primary and secondary coils being so inductivelycoupled and being so tuned by said tuning condensers as to pass a bandof frequencies having a comparatively low frequency.

6. A coupling network for passing signals in a high frequency band andin a low frequency band, said network comprising a high frequency bandpass circuit having a tuned primary circuit including a primary coil anda tuned secondary circuit including a secondary coil, at least oneinductance coil common to said circuits and coupling them the correctamount to give them a band pass characteristic, and a low frequency bandpass transformer having inductively coupled primary and secondary coils,said primary coils being connected in series and said secondary coilsbeing connected in series, and means for so tuning said low frequencytransformer as to give it a band pass characteristic without disturbingthe action of said high frequency band pass circuit in said highfrequency band.

'7. A coupling circuit for coupling two electric discharge tubes incascade, each of said tubes having an input circuit and an outputcircuit said coupling circuit comprising a primary coil connected to theoutput circuit of one of said,

tubes to form a primary circuit and a secondary coil connected to theinput circuit of another of said tubes to form a secondary circuit, saidcoils being coupled by means of a pair of inductance coils in parallelwith each other at high frequencies and common to the primary andsecondary circuits, said primary and secondary coils each having acapacity thereacross to tune them to pass a band of frequencies at acomparatively high frequency, a transformer having primary and secondarycoils which are highly inductive as compared with said rst mentionedprimary and secondary coils and said coupling coil, said primary coilsbeing connected in series in said output circuit and said secondarycoils being connected in series in `said input circuit, a tuningcondenser connected between said first primary coil and one of saidcoupling coils for tuning said second primary coil, a tuning condenserconnected between said first secondary coil and the other of saidcoupling coils for tuning said sec-` ond secondary coil, said tuningcondensers having such capacity that said transformer is tuned to pass aband of frequencies at a comparatively low frequency, a blockingcondenser connected in series with said tuning condensers and betweenthe high potential ends of said coupling coils, a diode and a resistorconnected in series with each other and in series .with saidsecondarles, and a condenser connected across said resistor, one of saidcoupling coils having its high potential end connected to the junctionpoint of said blocking condenser and said second tuning condenser andhaving its low potential end connected to the junction point of saidresistor` and said second secondary coil.

GUSTAVE L. GRUNDMANN.

